Treatment of steel



Dec. 1, 1953 R. J. WILCOX ET AL 2,661,279

TREATMENT OF STEEL Filed Sept. 8, 1951 //Y1/E/Yra)?5.

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Patented Dec. 1, 1953 UNITED STATES ATENT OFFICE,

TREATMENT OF STEEL Application September 8, 1951, Serial No. 245,742

3 Claims. 1

Our invention relates to the treatment of the high alloy or stainless steels. Our present application is a continuation-in-part of our copending application, Serial No. 182,834, filed September 1, 1950, now abandoned, which, in turn, is a continuation of our application, Serial No. 36,498, filed July 1, 1948, and now abandoned.

Prior to our invention, one of the very important unsolved problems in the alloy casting industry was the formation of voids, such as blisters, blow holes, and porosity, in the low carbon stainless alloys which were cast in green sand molds. Green sand, as commonly referred to in the foundry industry, is freshly made, water-tempered molding sand, molds from which are made and closed for pouring without special drying.

It was known that the formation of internal voids in these alloys was due to presence of gases,

especially hydrogen and probably also nitrogen, in the liquid metal. Moisture appeared to be the largest source of hydrogen and it came to be customary practice during the melting of these alloys to keep all materials entering into the process very dry, resorting to preheating, if necessary, and to take care that there were no water leaks of any kind in the furnace. In spite of this practice, the steel maker still found that his production was unpredictably and inconsistently defective due to the presence of entrapped gases. As a consequence, he was forced to resort to dry sand molding, i. e., molds which had been thoroughly dried to remove all traces of moisture, and the combination of the aforementioned careful melting practice with dry sand molding permitted these alloys to be successfully cast.

It will be seen, however, that the extreme precautions in melting and the use of dry sand molding are substantial items of expense in the casting of the stainless alloys. Furthermore, dry sand molding is much inferior to green sand molding from the standpoint of the production of closely fitting mold joints and intricate castings of good surface appearance.

Our invention resides in a method for treating the stainless alloys which prevents all traces of internal gas voids. It therefore permits a relaxation of the customary strict precautions for eliminating moisture from the furnace and, more importantly, it permits these alloys to be cast in 2 tellurium may be used in place of or with selenium with the same results.

Our invention may be compared to the use of aluminum additions in the production of carbon and low alloy steel castings. Just as in the stainless industry, it was for years unsafe to cast carbon steels in green sand molds. It was eventually found that aluminum additions deoxidized the steel so that green sand castings could be poured without danger of gas voids. Aluminum additions, however, are not especially useful in reducing voids in the stainless alloys inasmuch as the source of the voids is different in the stainless alloys than it is in carbon steels. In the stainless steels, the reducing gases, hydrogen and nitrogen, are the troublemakers; whereas, in the carbon steels, it is the oxidizing gases which are the source of gas voids.

Tests and, experience have shown that when used in the preferred amounts, hereinafter indicated, selenium and tellurium have no harmful or undesirable effects on the metal. This is to be contrasted with the use of aluminum in carbon steels where the result is often a sound steel but one which has lower physical properties. It is interesting to observe that one worker (Gagnebin, Patent No. 2,258,604) in the carbon and low alloy steel industry has found that these harmful effects of aluminum in carbon steels can be overcome by the use therewith of selenium or tellurium which he says coalesce the sulfides, a function ordinarily performed by the oxygen.

In addition to the prior use of selenium or tellurium in carbon and low alloy steels for the purpose just indicated, selenium has been used in the past as an additive for the purpose of improving machinability. This has always been in rather substantial amounts whereas in the practice of our invention, the purpose of which is to degasify the metal, it is desirable to limit the total quantity of selenium and/or tellurium added to 0.15% or less by weight of the metal. The most desirable range appears to be from about 0.005% to 0.03%. When quantities much in excess of 0.15% are used, undesirable results, such as lowered corrosion resistance, sluggishness of the molten metal, and poor weldability begin to occur. These are not noticeable, however, with the selenium and/or tellurium contents contemplated in this invention.

As already indicated, the selenium or tellurium are preferably added late in the melting operation. In induction furnaces, the addition is ordinarily made to the molten metal just prior to tapping the heat. In direct arc furnaces, the addi- 3 tion is ordinarily made to the ladle while the heat is being tapped. The selenium or tellurium may be added in the elemental form or as an alloy, such as ferro-selenium and ferro-tellurium which are preferred forms of additives.

As indicated, the invention is designed especially for castings of the low carbon stainless steel alloys such, for example, as ACI steels CF--8, CF-8M, CN-ZMCu. While finding its greatest use in the production of iron-nickel-chromium stainless castings, our invention can be profitably used in the production generally of heat and corrosion resistant alloys where gas voids caused by reducing gases are found and is especially useful when it is desirable to cast these alloys in green sand molds. It is contemplated that in certain instances the reducing gases may cause diiTculties in the production of carbon and low alloy steel products in which cases use of our invention is indicated, it being noted that ordinarily in this field the reducing gases are held below a harmful level by evolution during the boil of the molten bath. In all cases, it is preferable to use our additives in the amounts indicated above.

The drawing is a striking illustration of the effectiveness of small amounts of selenium in reducing internal voids-and similar results are obtained by the use of tellurium or a combination of the two elements. The drawing shows macro sections of two similar steel parts cast in green sand molds and prepared from the same electric furnace heat of steel having an analysis of C.073%, Si1.55%, Ni-11.43%, Cr-20.87%, the balance being substantially all iron. Just before pouring part 1 of the drawing 0.01% selenium was added to the ladle and it will be noted that the resulting product was sound and free from porosity or voids. However, no selenium addition was made to the metal forming part 2 and it is apparent from the immense void re vealed by the macrosection that considerable gas has been trapped in the metal. It is evident that the small selenium addition marked the difference between a process producing an acceptable casting and a process producing one which was not acceptable.

We claim:

1. A ladle treatment for corrosion and heatresisting steels of the iron-nickel-chromium type to reduce porosity and like defects which comprises adding to the molten steel in the ladle a degasifying agent consisting of at least one of the elements selected from the group consisting of selenium and tellurium, said element being in solid form and in an effective amount no greater than about 0.03% by weight of the steel.

2. A ladle treatment for corrosion and heatresisting steels of the iron-nickel-chromium type to reduce porosity and like defects which cornprises adding to the molten steel in the ladle a degasifying agent consisting of the element selenium in solid form in effective amounts no greater than about 0.03% by weight of the steel.

3. A ladle treatment for corrosion and heatresisting steels of the iron-nickel-chromium type to reduce porosity and like defects which comprises adding to the molten steel in the ladle a degasifying agent consisting of the element tellurium in solid form in effective amounts no greater than about 0.03% by weight of the steel.

RAYMOND J. WILCOX. FRANK G. VIHTELIC.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,846,140 Palmer Feb. 23, 1932 2,212,495 De Vries Aug. 27, 1940 2,236,716 Morris Apr. 1, 1941 2,253,502 Boegehold Aug. 26, 1941 

1. A LADLE TREATMENT FOR CORROSION AND HEATRESISTING STEELS OF THE IRON-NICKEL-CHROMIUM TYPE TO REDUCE POROSITY AND LIKE DEFECTS WHICH COMPRISES ADDING TO THE MOLTEN STEEL IN THE LADLE A DEGASIFYING AGENT CONSISTING OF AT LEAST ONE OF THE ELEMENTS SELECTED FROM THE GROUP CONSISTING OF SELENIUM AND TELLURIUM, SAID ELEMENT BEING IN SOLID FORM AND IN AN EFFECTIVE AMOUNT NO GREATER THAN ABOUT 0.03% BY WEIGHT OF THE STEEL. 